1000BaseBX WDM BiDirectional SFP Module TP-LINKs TL-SM321A adopts the latest standard 1000Base-BX, transmission over a single strand of fibre, with one different wavelength going in each direction. You can extend the network distance up to 10Km with TP-LINKs Routers, Switches, Media Converters to provide high speed and stability.Please note this item is non-returnable, see our returns policy for more information.